Interpreting Abnormal Pap Tests

Because a Pap test screens for abnormal cervical cells and because those cell changes can be associated with cervical cancer, being on the receiving end of an abnormal Pap test result can be frightening, intimidating, and confusing.

On the “frightening” aspect: Some people assume that an abnormal Pap means that cervical cancer is imminent. On the contrary, the National Cancer Institute not only states that cervical cancer, when it develops, takes “many years” to do so, but also that “[t]he majority of infections with high-risk HPVs [human papillomaviruses] clear up on their own.” This is not to suggest that regular screenings aren’t important — but rather, that they do their job and detect cervical changes in plenty of time to prevent cancer from developing in the first place.

Remember that if you’re confused about your Pap test results, part of your health care provider’s job is to answer your questions and keep you informed.

On the “confusing”: It’s true. There are a lot of different letter codes. Though some of them look awfully similar, they each mean a different thing. Moreover, the clinical recommendations for how to follow up with an abnormal Pap can depend not only on the code — in other words, the specific abnormal result — but also on one’s age and medical history.

Ready to sort them out?

Most labs in the United States use a classification system called the Bethesda System in order to have some standard terminology when reporting results. The Bethesda System uses the term squamous intraepithelial lesion to describe changes on the surface of the cervix. It categorizes those changes in these ways:

  • ASC-US or atypical squamous cells of undetermined significance, which is basically what it sounds like. There are some cells that appear abnormal, but clinicians can’t determine more specifically than that, and so some follow-up procedures may be recommended. According to the American College of Obstetricians and Gynecologists, for people age 20 and younger, a repeat Pap test in 12 months is recommended.** For people age 21 and over, follow-up recommendations include a repeat Pap at a shorter interval (6 to 12 months, depending on the source), an HPV DNA test (according to the American Society for Colposcopy and Cervical Pathology, this is the preferred option where available), or colposcopy. People who are pregnant may delay further testing until after birth.At Planned Parenthood Arizona health centers, labs automatically test any ASC-US results for HPV. If the HPV test is negative for high-risk strains, PPAZ physicians recommend having a repeat Pap test in one year. If the HPV test is positive for high-risk strains, the patient is referred for a colposcopy.
  • ASC-H or atypical squamous cells that cannot exclude a high-grade squamous intraepithelial lesion. Essentially, there are some cells that appear abnormal and clinicians aren’t completely sure what they mean — but in this case, they cannot exclude a high grade cervical change (see HSIL below). For this reason, the recommended follow-up is a colposcopy.
  • LSIL or low grade squamous intraepithelial lesions, or mild cervical changes that “almost always” indicate that HPV is present. Very common within abnormal results — and accounting for approximately 2.9 percent of all liquid-based results — LSIL usually goes away on its own without treatment. Because of this, repeat Pap testing is recommended for people under age 20. Colposcopy is recommended for people who are over age 21 and have not yet reached menopause, though people who are pregnant may delay further testing until after birth. In people who are menopausal, repeat testing, HPV DNA testing, and colposcopy are all considered “[a]cceptable options.”
  • HSIL or high grade squamous intraepithelial lesions. As the National Cancer Institute explains, “High-grade means that there are more evident changes in the size and shape of the abnormal (precancerous) cells and that the cells look very different from normal cells.” According to a study published by the American Journal of Obstetrics and Oncology, because these cell changes are the most likely — if left untreated — to progress to cancer, recommendations for most populations involve proceeding directly to a colposcopy. Moreover, for someone who is over age 21 but is not pregnant, health care professionals may prefer to proceed directly to removing the abnormal cells via LEEP.
  • AGC or atypical glandular cells. While these types of cell changes can be caused by benign issues like polyps, they may also indicate precancer in the upper part of the cervix, the endometrium, the ovaries, or the fallopian tubes. Because atypical glandular cells can indicate a variety of different issues, the initial follow up also involves multiple tests. For non-pregnant people of any age, the ACOG’s recommendations include colposcopy with endocervical sampling, HPV testing, and endometrial evaluation (which may include endometrial sampling). For people who are pregnant, endometrial and endocervical sampling should be deferred.

Even more than knowing what any individual result means, it’s important to remember that if you’re confused about your Pap test results, part of your health care provider’s job is to help ensure that you’re fully informed about the state of your health (cervical and otherwise), the implications, and the possible courses of action. If, for whatever reason, you can’t recall this list word-for-word when you’re on the phone with a medical assistant or in a paper gown on an exam table — it’s always your right to ask!

** This fact sheet was published in May 2011. Additionally, while most relevant health care associations in the United States now recommend against general screening for people under age 21, there are some people (for example, those who are immunocompromised) for whom earlier screening may be appropriate on a case-by-case basis.